In many industries it is desirable to measure the relative displacement of one body or surface to another. Possible application includes the measurement of relative displacement of adjacent monoliths or parts of structures such as: generator bays in powerplants, tunnel liner monoliths, displacement at stress cracks in structures, continuing displacement monitoring at geologic faults in underground cavities or surface foundations, monitoring alignment of machinery, and measuring strain through displacement.
The prior art reveals a number of means by which the displacement of one surface or body with respect to another surface or body may be detected or measured. For example, U.S. Pat. No. 3,842,509 discloses a strain gauge ambiguity sensor that detects variations in the planar adjustment of mirror segments through the use of a bendable mechanical element and electronic means to sense when that element is bent. This type of device is limited to areas where the relative displacement is fairly minimal, as the resistive elements acting to detect displacement can only be bent through a limited arc. The device also offers no detection means for purely lateral movement.
Polish Pat. No. 48889 discloses a feeler gauge for measuring the reciprocal shift between two block structures. The apparatus does allow measurement of the relative motion in all three planes of movement, however, as the gauge instrument is held snug in the measurement apparatus, little flexibility is afforded. Therefore, the apparatus is farily limited to situations where the relative displacement is minor.
The prior art thus reveals a common fault. The prior devices are limited to surfaces in substantial harmony with one another, and does not provide flexibility of application nor ease of operation.
There is, consequently, a need for an apparatus capable of measuring the relative displacement between two bodies in three dimensions while not limited to very small relative displacement between the bodies and easily adapted to numerous applications. The present invention is directed to that need.